Pumping system for evacuating gas from a plurality of chambers and method for controlling the pumping system

ABSTRACT

A pumping system for evacuating gas from a plurality of chambers, includes at least one turbomolecular pump, at least two fore-vacuum pumps, at least one connection conduit extending between the at least two fore-vacuum pumps. and at least one transverse constriction for at least one of reducing and regulating gas flow.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a pumping system for evacuating gas from a plurality of chambers and to a method of controlling the pumping system.

2. Description of the Prior Art

Practically, the entire system consists of one or more vacuum chambers (recipients). These chambers can be used separately, however, they may be connected, at least partially, with each other. In this case, at a set pressure difference, a substantial gas flow takes place therebetween through an opening formed in a common wall between two process chambers or through a tubular conduit connecting the chambers. One or several chambers can also be subjected to gas loads which can also result from connection with the chamber environment (atmosphere), from gas loads transmitted from upstream-located chambers, from otherwise generated, mostly process-dependent, gas flows, and also from admitted inert or process gases such as helium, from desorption from workpieces, test pieces placed into a chamber, and/or chamber components, and/or from reaction products actively produced in a process.

In order to maintain the process in each chamber, the chambers should be evacuated by respective vacuum pump systems connected therewith at a predetermined vacuum that should be maintained as constant as possible. The separate vacuum pump systems are formed either of a separate pump or of several pumps which are connected seriesly or parallel to each other. Dependent on the gas flow, several chambers can be simultaneously evacuated by a single pump or by several pumps with a common fore-vacuum pump. The connections between the chambers and the pumps can be formed as series connections, parallel connections, or any arbitrary combinations of those connections.

The state-of-the-art (WO2011/121322A2) discloses that pumps can be arranged in suitable manner so that they mutually support each other, with the pumps being connected to a different pressure level within the other pump.

For the most part, the processes in multi-chambers systems require a high gas load at a low pressure, so that there large fore-vacuum pumps must be used in order to be able to maintain a desired vacuum. The low pressure means that a high suction capacity need be available. Simultaneously, other chambers of such a system can maintain vacuum with very small expenditures, and a smaller pump can suffice. The greater is the gas load a pump should handle, the higher is the energy consumption and the associated therewith cooling requirements, and electrical and mechanical losses caused by gas friction.

Because of environmental and boundary conditions, e.g., a limited constructional space, allowable heat output, noise and vibration generation, it can be advantageous to use several small pumps instead of a large one. It is further advantageous to be able to distribute the loads as uniformly as possible to insure a high efficiency of the pumps.

In actual cases, the gas loads and vacuum differ greatly from chamber to chamber, and adaptation of the noise reduction to existing possibilities while maintaining the desired process characteristics, is difficult and only possible when considering the balance of interests. One type of solution is described in the state-of-the art (WO2011/121322 A2). However, the proposed solution requires the use of special pumps with matching intermediate connections.

The object of the invention is a system which permits to optimally use a largest possible number of pumps from the economical and technical standpoints, and to distribute the existing gas loads as uniformly as possible between a number of as simple as possible and similar or identical pumps, without retroactive effects on the process.

SUMMARY OF THE INVENTION

The object of the invention is achieved by a pumping system for evacuating gas from a plurality of chambers, including at least one turbomolecular pump, at least two fore-vacuum pumps, at least one connection conduit extending between the at least two fore-vacuum pumps, and at least one transverse constriction for reducing and/or regulating gas flow; and by a method including measuring vacuum or gas flow rate at a point of the at least one chamber, in the at least one conduit, and pump connections provided to that end, and using the at least one of measured variables for controlling the at least one transverse constriction.

According to the invention, the maximum gas flow in at least one of respective conduits, which connect a plurality of pumps connected seriesly and/or parallel to each other, is limited by at least one transverse constriction. Within the meaning of the invention, the transverse constriction is also understood as a device that completely closes the conduit.

The transverse constriction can be formed advantageously as a simple throttle orifice. It represents a constructional component having a definite transverse constriction over a predetermined length of the available conduit.

In a simplest case, the flow-restricting orifice meter is provided with a stationary constriction.

According to a further, particularly advantageous embodiment, the constriction is adjustable within a certain region. In this embodiment, the constriction is in form of a throttle valve. The adjustable region can be adjusted mechanically by a hand or electrically, pneumatically, or hydraulically by a control drive.

The adjustment of the throttle valve is carried out advantageously based on a previously determined calibrated scale. However, there is no feedback of an actual cross-section of the exemplary gas flow. To this end, advantageously, a separate or integrated gas flow measurement follows, so that in order to be able to regulate a predetermined gas flow, it is possible to form a closed regulating circuit. For the most part, a corresponding pre-set value is generated electrically as an analogue electrical signal, e.g., voltage, current, pulse modulation, or by another conventional method, or is transmitted as a digital signal by an arbitrary bus system. Alternatively or additionally, the target can be produced by a local or remote control unit with a user interface. This device is generally called a gas flow controller. The gas flow controller is a customary component that is also called a mass flow controller.

The above-mentioned transverse constrictions can be formed suitably as separate constrictions or as a combination of identical or different constrictions arranged seriesly and/or parallel to each other. The use of one or several valves for separating one or several conduit sections of a formed network additionally expands the possibilities for adaptation to different process conditions.

According to a further advantageous embodiment of the invention, there exists a possibility to measure the vacuum and/or the gas flow rate at one or several points in one or several chambers, and/or at arbitrary points inside of the conduits, or at pump connections provided to this end, and to use the obtained values for regulating the above-mentioned parameters. The simplest embodiment discloses a pressure switch that generates a signal for opening or closing a conduit section at a predetermined threshold pressure to prevent overload of the connectable pump or the influence of process parameters.

According to yet another advantageous embodiment of the invention, a superordination process control is contemplated. With a superordination process control, it is possible to use obtained, at different locations, measurement data for process evaluation and for influencing the process and, thereby, to optimize the process and the load of separate pumps.

When pumps are used the pump throughput of which depend, at least partially, on the discharge pressure, e.g., with the use of turbomolecular pumps, it is advantageous when those have, at their discharge side, a pump stage that delivers a constant throughput over a large pressure region.

This stage may include, e.g., Gaede, Siegbahn, and/or Holweck stage. The robustness of a pump against pressure fluctuation at the discharge side permits to noticeably simplify the lay-out of the system. Thereby, it is possible to operate with a simple throttle orifice instead of a switchable or regulated valve.

The invention permits not only to prevent use of pumps the dimensions of which vary greatly, but rather permits to use two or more identical pumps at different positions to thereby keep the number of different pump types in production, sale, assemblies, and use low and, thereby, to reduce manufacturing costs and provide cost savings for customers. The cost savings are achieved due to low qualified expenditures. Qualified expenditures mean that the user installs and tests several pumps of the same type which pumps in combination are best able to meet the job requirements at the region-specific predetermined network voltage or the region-specific network frequency. This approach is applicable to both pumps in the fore-vacuum region as used in the above example, and pumps connected directly or by connection conduits with respective chambers.

The described solution provides many advantages with systems, e.g., so-called LCMS-systems, in which the pumps with a small load must pump, at least in one process condition, primarily light gases (small particle mass) as, e.g., at additional gas load, when helium is used as a process gas. The pumping capacity according to main pump principles depends on to-be-pumped atom, e.g., molecular weights. Light gases with small masses are generally more difficult to pump. The pumping capacity of such pumps sharply increases when heavy gases, such as drag medium, are used. In this case, the heavy particles drag the light particle in the correct direction through the pump, thus reducing the backflow of the light particles. While the pump generally must pump more gas, the pump throughput of light gases noticeably increases. The discharge of the first pump, which feeds, through a transverse constriction, a gas flow with a smaller portion of light gases to the second pump, causes a corresponding drag effect in the second pump that in the described case, pumps gas with a high content of light gases, so that the light gases can be pumped noticeably better.

Pumps, which are connected to a local power supply, are often driven by a frequency converter, and rotate, dependent on to the region-specific network frequency (typically 50 Hz or 60 Hz) or network voltage (typically 90V, 120V, 230V), with a different speed and/or with a different maximal input power (e.g., due to limitation of the driving current or the resulting heat input) and change, thereby, correspondingly their maximal pump throughput. This leads to that chambers which are evacuated directly by such a pump, are pumped, dependent on an available power supply network, at a different pressure level. In order to prevent this, according to a conventional practice, up to now it was necessary to so regulate the gas flow by adaptation of the stop-throttle valves or orifice meters within or on the chambers that at an available or predetermined power supply network, the desired process pressure is achieved. Because of the complexity of the entire system, this is not easily realized and is connected with high costs because for the most part, several corresponding chambers are involved. This problem is solved by providing, according to the invention, a transverse constriction between the concerned first pump with a variable rotational speed and/or variable input power, and second pump that either pumps a region in which the chamber pressure is irrelevant, and/or a pump directly connected with the chambers, e.g., one or several turbomolecular pumps which produce a fore-vacuum pressure, wherein those are robustly react against pressure changes at their discharge side. A simple change or adjustment of the above-mentioned transverse constriction equalizes the difference in the pump throughput of the first pump so that the concerned chamber pressure remains constant, without a need to undertake any measure in or outside the chamber. Such adjustment can be undertaken, as it has already been described, with internally or externally connected control units that determine the process condition, e.g., the vacuum in the concerned chamber, and adjust, by adjusting the transverse constriction, the vacuum to a value desired for an actual process condition.

The object of the invention can also be achieved by varying the pump through-put based not on the influence of the power supply network but rather on the difference in the operational conditions of the pump, e.g., on heat generated during operation or on changing environmental conditions, in particular, on the environmental and/or cooling water temperature, and also on different pump throughputs.

A conventional embodiment has two or more chambers which at least partially connected with each other and, for the most part, operate at different vacuum. Gas flows are produced by the fed to-be-analyzed gases and often, by the auxiliary gases delivered in another chambers. Alternatively, the vacuum in one or several chambers is produced directly with a fore-vacuum pump. Otherwise, one or several chambers is (are) evacuated by one or more turbomolecular pumps which are supported again together and/or separately by one or more fore-vacuum pump(s). Alternatively, at least one of the vacuum pumps can have more than one inlet (split flow, interstage port) connected with at least one other chamber and the first inlet of the pump. Advantageously, the pumps have a high robustness against the high discharge pressure. Typically, the pressure difference between the turbomolecular pump and the fore-vacuum pump lies in a region from 1 to 20 mbar. To relief at least one of the at least two fore-vacuum pumps, there is provided at least one connection with a transverse constriction between the suction connectors of the first-mentioned fore-vacuum pump and the second fore-vacuum pump, and which provides maximum for such gas flow that the second fore-vacuum pump always can be retained at a certain discharge pressure. The first, relief fore-vacuum pump can be selected smaller than the second one so that the second one can be better used.

The novel features of the present invention, which are considered as characteristic for the invention, are set forth in the appended claims. The invention itself, however, both as to its construction and its mode of operation, together with additional advantages and objects thereof, will be best understood from the following detailed description of preferred embodiments, when read with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS:

The drawings show:

FIG. 1 a schematic view of a prior art pumping system;

FIG. 2 a schematic view of a first embodiment of a pumping system according to the present invention;

FIG. 3 a schematic view of a modified embodiment, in comparison with first embodiment, of a pumping system according to the present invention;

FIG. 4 a schematic view of a further modified embodiment of a pumping system according to the present invention;

FIG. 5 a schematic view of a still further modified embodiment of a pumping system according to the present invention;

FIG. 6 a schematic view of yet a further modified embodiment of a pumping system according to the present invention;

FIG. 7 a schematic view of another further modified embodiment of a pumping system according to the present invention; and

FIG. 8 a schematic view of yet another modified embodiment of a pumping system according to the present invention;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

FIG. 1 shows a prior art pumping system that has two to-be-evacuated chambers 1 and 2. A turbomolecular pump 3 is associated with the chamber 1, and a turbomolecular pump 4 is associated with the chamber 2.

The turbomolecular pump 3 is supported by a fore-vacuum pump 5, and the turbomolecular pump 4 is supported by fore-vacuum pump 6. The drawback of the prior art pumping system consists in that the turbomolecular pump 3 should maintain a predetermined pressure in the chamber 1, and the turbomolecular pump 4 should maintain a predetermined pressure in the chamber 4. Accordingly, the pumps 3, 4, 5, 6 should be correspondingly capable of performing this task. This means that they must have a required pumping capacity under network voltage and frequency condition for a particular region.

Q designates a gas flow. The chambers 1 and 2 are connected with each other. With different pressures in chambers 1 and 2, there exists a gas flow Q between the two chambers. In the chamber 2, in addition, there is provided a gas inlet 7 for feeding a process gas into the chamber 2.

FIG. 2 shows two chambers 1, 2 which are evacuated by turbomolecular pumps 3, 4.

Fore-vacuum pumps 5, 6 provide support for turbomolecular pumps 3, 4. A conduit 8 is provided between the fore-vacuum pumps 5 and 6. In the conduit 8, a throttle orifice 9, which is shown schematically, is arranged. The throttle orifice 9 permits to control the gas flow in the conduit 8.

By the arrangement according to the present invention, it is possible to identically dimension the pumps 3, 4, e.g., to use turbomolecular pumps 3, 4 of the same type. This results in relief of the first pump 5 that delivers, via the throttle orifice 9, a gas flow with a smaller portion of light gases to the second pump 6. This leads to a drag effect in the second fore-vacuum pump 6 that, according to FIG. 2, pumps a greater portion of light gases, so that the light gases can be pumped noticeably better.

The same is true for the arrangement in FIG. 3, wherein a single turbomolecular pump 4 is provided for evacuation of chamber 2.

The chamber 1 is evacuated by the fore-vacuum pump 5. For supporting the turbomolecular pump 4, the fore-vacuum pump 6 is provided.

Again, a conduit 8 extends between the fore-vacuum pumps 5, 6 and is provided with a throttle orifice 9.

FIG. 4 shows a modified embodiment with three chambers 1, 2, and 10. As shown in FIG. 4, again, there are provided two fore-vacuum pumps 5, 6 and a turbomolecular pump 3 for evacuation of chamber 1. For evacuation of chambers 2 and 10, a split-flow pump 11 is provided. The split-flow pump 11 has two inlets 12 and 12 a. Again, a conduit 8, which is provided with a throttle orifice 9, extends between the fore-vacuum pumps 5 and 6.

FIG. 5 shows a further modified embodiment with six to-be-evacuated chambers 1, 2, 10, 13, 14, 15. The chambers 2, 10, 13 have additional gas inlets 16, 17, 18 for process gases.

For evacuation of the chamber 1, a turbomolecular pump 3, which is supported by a fore-vacuum pump 5, is provided. For evacuation of chambers 2, 13, and 14, a split-flow pump 19 is provided. The split-flow pump 19 is supported by a fore-vacuum pump 6.

An additional turbomolecular pump 20 is provided for evacuation of the chamber 15.

A conduit 8 with a throttle orifice 9 extends between the fore-vacuum pumps 5 and 6. Here likewise, a relief of the first fore-vacuum pump 5 is provided and which delivers a gas flow with a smaller portion of light gases to the second fore-vacuum pump 6 as a result of a transverse constriction in form of the throttle orifice 9 provided in the conduit 8 connecting the fore-vacuum pumps 5 and 6. This leads to a drag effect in the second fore-vacuum pump 6 that, in this case, pumps a greater portion of the light gases, so that light gases can be pumped noticeably better.

FIG. 6 shows an arrangement with four chambers 1, 2, 10, 13. The chamber 1 is evacuated by a turbomolecular pump 3, and the chamber 2 is evacuated by a turbomolecular pump 4. The turbomolecular pump 3 is supported by a fore-vacuum pump 5, and the turbomolecular pump 4 is supported by a fore-vacuum pump 6.

A conduit 8 with a throttle orifice 9 extends between the fore-vacuum pumps 5 and 6.

For evacuation of the chambers 10, 13, a split-flow pump 11 is provided and which is supported by a fore-vacuum pump 21. An additional conduit 22 is provided between the fore-vacuum pumps 6 and 21 and has a throttle orifice 9.

FIG. 7 shows a pump arrangement for a multi-chamber system with six chambers 1, 2, 10, 13, 14, 15. The chambers 1, 2, 13, 14, 15 are evacuated by constructively identical turbomolecular pumps 3, 4, 20, 24, 25. The turbomolecular pump 3 is supported by a fore-vacuum pump 5. The pumps 4, 20, 24, 25 are supported by a fore-vacuum pump 6. Again, a conduit 8 with a throttle orifice 9 extends between the fore-vacuum pumps 5 and 6.

FIG. 8 shows a multi-chamber system with six chambers 1, 2, 10, 13, 14, 15. The chamber 1 is evacuated by a fore-vacuum pump 5. Constructively identical turbomolecular pumps 4, 20, 24, 25 evacuate the chambers 2, 13, 14, 15. The pumps 4, 20, 24, 25 are supported by a fore-vacuum pump 6.

A conduit 8 with a throttle orifice 9 extends between the fore-vacuum pumps 5, 6. A device 26 for measuring an actual vacuum is provided in the chamber 14.

A device 27 for measuring an actual vacuum is mounted on the pump 20 on the connection provided to this end.

A device 29 for measuring a gas flow rate is provided in a conduit 28. A device 30 for measuring a gas flow rate is provided in the conduit 8.

Though the present invention was shown and described with references to the preferred embodiments, such are merely illustrative of the present invention and are not to be construed as a limitation thereof and various modifications of the present invention will be apparent to those skilled in the art. It is, therefore, not intended that the present invention be limited to the disclosed embodiments or details thereof, and the present invention includes all variations and/or alternative embodiments within the spirit and scope of the present invention as defined by the appended claims. 

What is claimed is:
 1. A pumping system for evacuating gas from a plurality of chambers, comprising at least one turbomolecular pump; at least two fore-vacuum pumps; at least one connection conduit extending between the at least two fore-vacuum pumps; and at least one transverse constriction for at least one of reducing and regulating gas flow.
 2. A pumping system according to claim 1, wherein the at least one transverse constriction is formed as an adjustable constriction.
 3. A pumping system according to claim 1, comprising a further turbomolecular pump constructively identical to the at least one turbomolecular pump.
 4. A pumping system according to claim 1, wherein at least one transverse constriction is formed as one of throttle orifice, throttle valve, and gas flow controller.
 5. A pumping system according to claim 1, wherein the at least one transverse constriction is formed as one of regulated and switchable valves.
 6. A pumping system according to claim 1, comprising a plurality of transverse constrictions switchingly arranged one of seriesly and parallel to each other.
 7. A pumping system according to claim 1, wherein there is provided a superordination process control for regulating the at least one transverse constriction.
 8. A pumping system according to claim 1, wherein a device for measuring one of actual vacuum and gas flow rate is provided at least at one of a point of at least one chamber of the plurality of chambers, in the at least one conduit, and pump connections provided to that end.
 9. A pumping system according to claim 1, wherein the at least one turbomolecular pump is formed as an exhaust pressure-dependent pump.
 10. A pumping system according to claim 1, wherein the pumping system is designed for evacuating gas from a plurality of chambers comprising at least two chambers connected with each other.
 11. A pumping system according to claim 10, wherein one of the at least two fore-vacuum pumps is located immediately adjacent to one of the at least two chambers.
 12. A pumping system according to claim 1, comprising a plurality of turbomolecular pumps, wherein at least one of the fore-vacuum pumps is arranged in front of at least one of the turbomolecular pumps.
 13. A pumping system according to claim 1, comprising a plurality of turbomolecular pumps, and wherein the at least two fore-vacuum pumps are arranged, at least one off together and separately, in front of one of a part of the turbomolecular pumps and all of the turbomolecular pumps.
 14. A pumping system according to claim 1, comprising a plurality of turbomolecular pumps, and wherein at least one of the plurality of turbomolecular pumps has two inlets.
 15. A method of controlling a pumping system for evacuating gas from a plurality of chambers, comprising at least one turbomolecular pump; at least two fore-vacuum pumps; at least one connection conduit extending between the at least two fore-vacuum pumps; and at least one transverse constriction for at least one of reducing and regulating gas flow, the method comprising the steps of measuring one of vacuum and gas flow rate at at least one of a point of at least one chamber, in the at least one conduit, and pump connections provided to that end; and using the at least one of measured variables for controlling the at least one transverse constriction. 